1. Field of the Invention
The present invention relates to a method of manufacturing a rolling element string in which a number of rolling elements are aligned and rollably held in a row at prescribed intervals, and which is used by integrating, for example, in a linear guide device for endless sliding. More specifically, the invention relates to an improved rolling element string the tensile strength and the flexural strength of which are enhanced.
2. Description of the Related Art
Conventionally, the known linear guide device for guiding a movable body such as a table along the fixed portion such as a bed is of the type that comprises a rollway having a ball rolling groove, a slider having a loaded rolling groove opposed to the ball rolling groove and a no-load rollway in which the ball is circulated from one end to the other end of the loaded rolling groove and moving along the rollway, and a number of balls rolling between the slider and the rollway under loaded conditions and circulating along the endless raceway composed of a loaded rolling groove and a no-load rollway of the slide.
In the conventional linear guide device in this arrangement, since the endless raceway of the slider is filled with balls, when the slider moves along the rollway, the adjacent balls tend to collide with or rub against each other as they circulate along the endless raceway, which results in earlier abrasion of balls and shorter operational life of the device.
Therefore, in order to solve the problem described above, a linear guide device incorporating a rolling element string having a plurality of balls aligned in a row into the endless raceway has been proposed (Japanese Patent Laid-Open No. 5-52217). As shown in FIG. 17 and FIG. 18, the rolling element string 100 comprises ball retaining members 102 interposed between the respective adjacent balls 101 and is constructed in such a manner that the balls are linked consecutively by linking the respective ball retaining members 102 with a pair of belt members 103 disposed in the direction of alignment of the balls 101, and is manufactured by injection molding of a flexible resin with the balls 101 disposed in a mold as cores.
In the conventional rolling element string 100 arranged in such a manner being incorporated into the endless raceway 105 and circulating along the endless raceway as shown in FIG. 19, since the ball retaining members 102 are interposed between the respective adjacent balls 101, friction or collision between balls are prevented from being occurred and abrasion of the balls 101 could be avoided as much as possible.
However, in the conventional method, since an elongated rolling element string of the length corresponding to an orbit of the endless raceway is manufactured by injection molding, there has been a problem in that a number of gates for injecting molten resin into a cavity in the mold must be provided to make the belt member 103 for linking the respective ball retaining members 102 form in a uniform thickness, whereby the mold becomes complex and the cost increases.
There has been another problem in that considering further downsizing of the linear guide device requires the thinner belt member for the rolling element string to be incorporated in the endless raceway, and decrease in the tensile strength and the flexural strength of the belt member associated with thinning thereof may cause breakage of the rolling element string in the endless raceway, thereby impairing the ball retaining capability of the rolling element string.
There has been still another problem in that when contemplating further thinning of the belt member, the molten resin injected from the gate may not reach the deepest portion of the cavity in the mold, thereby resulting in a number of defective moldings and thus reducing yields.
The present invention is directed toward the problems described above, and accordingly, it is an object of the present invention to provide a method of manufacturing a rolling element string in which further downsized rolling element string may be manufactured easily at low cost, and in which the rolling element string having superior tensile strength and flexural strength may be manufactured even after downsizing.
In other words, the present invention is a method of manufacturing a rolling element string having a number of rolling elements aligned and rollably held in a row at prescribed intervals comprising a first step of forming a flat band shaped belt member with a synthetic resin, a second step of forming retaining holes aligned in a row on the belt member for receiving rolling elements loosely, and a third step of placing the rolling elements in the respective retaining holes, forming spacer portions between the respective adjacent retaining holes for retaining the rolling elements therein by injection molding with these rolling elements used as cores, and trapping the rolling elements within the retaining holes.
According to the method of the present invention, since the spacer portions are formed after the flat band shaped belt member is molded in the first step, and then the rolling elements are trapped within the retaining holes formed on the belt member, the belt member may be formed consecutively in a long strip for example by extrusion molding of a synthetic resin, not by injection molding. Therefore, even when the thickness of the belt member is reduced in association with downsizing of the rolling element string, the belt member of uniform thickness may be formed stably.
In addition, since the belt member and the spacer portions are formed separately, the belt member can be formed of a synthetic resin material that is completely different from a molding material used for the spacer portions. Therefore, by forming the belt member with a synthetic resin the tensile strength or flexural strength of which has been improved by adding, for example, carbon filler, the rolling element string of high tensile strength may be manufactured even if the thickness of the belt portion is reduced. On the other hand, since the spacer portions are to be kept in slide-contact with the rolling elements, the material for the spacer portions may be selected to have a low friction coefficient such as oleoresin, thereby ensuring smooth rotation of the rolling elements.
It is also possible to integrate a reinforcing material such as a carbon fiber or a glass fiber along the length of the belt member as the belt member is formed by extrusion molding, whereby the tensile strength of the belt member can be increased even when the tensile strength or flexural strength of the synthetic resin constituting the belt member is low.
As is described thus far, according to the method of manufacturing the rolling element string of the present invention, since the spacer portions for retaining the rolling element within the belt member are formed by injection molding after the belt member for aligning the rolling elements is molded, the belt can be consecutively formed in a long strip by extrusion molding, but not by injection molding, whereby the belt member of a uniform thickness may be formed easily at low cost even when the thickness of the belt member is reduced in association with downsizing of the rolling element string.